SELECT id, title, url, score
WHERE timestamp > '2019-01-01'
AND REGEXP_CONTAINS(url, '.pdf|arxiv.org')
ORDER BY score desc
I'd think a better algorithm would be that if you upvote an article in the "new" section that eventually makes it to the main page, you'd get at least as many points as the submitter.
What I do to find my share of interesting links is to search on https://hn.algolia.com with different keywords and sift through those discussions, follow links in the comments, follow the commentators previous submissions and posts, follow other submissions from the website, gather new keywords and search again... it is kind of a rabbit hole once you start. Though you'd quickly begin to realise that it is great folks continue to submit links that don't end up hitting the front-page, as the aggregation of links is valuable even though the discussion is missing .
That said, I have stumbled upon a lot of interesting things aren't simply shared at all on news.yc, though, I guess this is by design. I just hope folks don't stop sharing links just because their previous submissions didn't generate discussion or upvotes on news.yc.
 Some would argue that few news.yc comments are worth their weight in upvotes anyway: https://danluu.com/hn-comments/
Getting to the front page isn't predictable, it's like creating a hit song. Tons of great music gets unnoticed. There's bias and well known names have an advantage.
If you want an awesome PDF reader to read these you should check out Polar :)
Yes. There's a Linux version! ;)
One caveat is that some stories have multiple submissions; I just linked to the one with the highest score for now, but will need to iterate a bit to better handle multiple submissions.